With the development by the National Aeronautics and Space Administration (NASA) of the Orbital Maneuvering Vehicle and the Space Station, there has been an increasing need for a completely automated rendezvous and docking system. Many future missions into space that have been planned involve rendezvous and docking scenarios that are impossible, risky or uneconomical if ground piloted control of the docking procedure is used. For example, the Mars Rover Sample Return (MRSR) mission planned by NASA will be impossible to control from Earth because of the long time delays involved. Even operations taking place in Earth orbit are subject to time delays on the order of several seconds as well as to disruptions beyond the control of the control station on Earth.
In the past, almost all vehicle docking operations have employed a human pilot to control the vehicle during the last roughly 1000 feet of the vehicle trajectory. The job of the pilot generally involves visually judging the relative position and attitude using an optical alignment sight and determining the maneuvers needed to align the vehicles based on his intuitive understanding of the dynamics involved. Although radar data and inertial measurement unit (IMU) data ar often available to the pilot so as to provide him with more accurate information about his position and attitude, the burden is on the pilot to visually estimate the attitude of the passive (target) vehicle relative to his own active (chase) vehicle. Further, some vehicles include three-axis (roll, pitch and yaw) autopilots to assist in maintaining vehicle attitude. However, these autopilots are not capable of generating the control signals necessary for translation (x, y and z -axis) maneuvers.
It will be appreciated that docking of vehicles using a human pilot involves a number of disadvantages in addition to those discussed above in connection with complex future missions now being planned. These disadvantages include the inherent limitations on the accuracy of a pilot's estimates with respect to geometrical relations, i.e., angles and distances, a lack of repeatability, and the potential for human error. Such considerations must be factored into vehicle design as well as mission planning, in order to ensure that the required margin of safety is provided and thus necessarily results in increased costs and decreased operational flexibility. For example, docking mechanisms must be over-designed in order to withstand impacts at high velocities that may occur with pilot error and the capture envelope must similarly be large. Further, a control station appropriate to the mission must be designed, constructed and tested, and it will be understood that such facilities are generally complex and costly due to the quantity and quality of the instrumentation needed to present accurate, timely information to the pilot. Further, time-consuming "pilot-in-the-loop" simulations must be performed to verify to the suitability of the information provided by the control station to the needs of the pilot in both normal and contingency situations.
It is also noted that if the mission is to be flown unmanned, a communications link must be established to provide the pilot with relevant data from the chase vehicle. Such links usually require a wide bandwidth because both high rate telemetry and video displays are normally needed by the pilot, and hence such links tend to be costly. Also, as mentioned above, the end-to-end time delay introduced by the communications link will degrade the performance of the pilot in docking the chase vehicle, thereby increasing the chances of failure. In this regard, for interplanetary missions such as the MRSR mission referred to above, the end-to-end delay is usually of such a magnitude that remotely piloted docking operations are simply not feasible.
Preliminary work this field relating to autonomous docking systems includes that described in Tietz, J. C. and Kelley, J. H.: Development of an Autonomous Video Rendezvous and Docking system, Martin Marietta Corporation, Contract No. NAS8-34679,Phase One, (Jun. 1982); Dabney, Richard W.: Automatic Rendezvous and Docking: A Parametric Study. NASA Technical Paper No. 2314, (May 1984); Tietz, J. C. and Richardson, T. E.: Development of an Autonomous Video Rendezvous and Docking System, Martin Marietta Corporation, Contract No. NAS8-34679, Phase Two, (Jun. 1983); and Tietz, J. C.: Development of an Autonomous Video Rendezvous and Docking System, Martin Marietta Corporation, Contract No. NAS8-34679, (Jan. 1984).